Audio amplifier



FIG. 1 is a front view of an audio amplifier.

FIG. 2 is a rear view of the audio amplifier shown in FIG. 1.

FIG. 3 is a top view of the audio amplifier shown in FIG. 1; and,

FIG. 4 is a bottom view of the audio amplifier shown in FIG. 1.

The broken lines show elements of the audio amplifier that form no part of the claimed design. 

I claim the ornamental design for an audio amplifier, as shown and described. 